The invention relates to the production of X-ray images utilizing fluoroscopy apparatus with a radiation source which alternately emits X-radiation produced with a high X-ray tube voltage and with a low X-ray tube voltage, and an X-ray image intensifier television chain which includes an X-ray image intensifier, a video camera, and a video display unit, with the video camera supplying respective first and second image signals resulting respectively from X-radiation produced with the high tube voltage and produced with the low tube voltage. Such an installation is known, for example from U.S. Pat. No. 3,229,089.
The constrast range of X-ray television images or other electronic X-ray images to be rendered visible on a television display unit is less than in the case of records with X-ray films. In the case of images with soft X-radiation, contrasts of soft parts, i.e. details absorbing X-rays only little, are well represented. Fine contrasts of locations which are penetrable with difficulty for X-rays, for example such in the region of bone shadows, therefore, become lost. On the other hand, with hard X-radiation, soft parts are irradiated without significant absorption and result in surface elements which appear structurelessly white in the image. Hard ray fluoroscopy images of bones, however, appear clear and contrasty. Therefore, also a careful selection of the hardness of the rays employed for the image in the case of a heterogenously composed specimen, such as e.g. a human body to be examined represents, as a rule, does not lead to any television image which is fully satisfactory in all parts.
In order to overcome the above-cited disadvantage, an X-ray imaging system has become known from U.S. Pat. No. 3,229,089 which contains means for generating coincident X-rays of different wavelengths with which a sample is irradiated alternately and repetitively. Moreover, means for the conversion of the X-ray images into a light image are provided, whereby the conversion takes placed in a television pickup-and-display arrangement which produces color images. In the color image a specific color is associated with each X-ray hardness. Moreover, the sequence of the images of different colors, i.e. hardness, is so controlled that no resolution is possible any longer by the eye. Accordingly, as the sum image such an image appears in which the details appear in different colors. However, an arrangement of this type has not yet been able to be successful in X-ray examination technology because no reality is attributed to the different colors. Moreover, the outlay is very great on account of the required synchronization.